Proof of the alleged trip would lend support to the Steele dossier ― the report by former British intelligence official Christopher Steele containing allegations that the Trump campaign conspired with the Russian government to win the election. (The dossier is also how we know about the alleged “golden shower thing.”) Hillary Clinton’s presidential campaign and the Democratic National Committee hired the firm that retained Steele to compile opposition research on Trump.

According to the dossier, Cohen played a part in the alleged conspiracy. It says he used a meeting with a Russian nongovernmental organization as cover to meet with Russian officials during a trip to Prague in August or September 2016. They allegedly discussed a “coverup and damage limitation operation in an attempt to prevent the full details of Trump’s relationship with Russia being exposed,” and discussed how to make “deniable cash payments” to “Romanian hackers.”

In his tweet on Saturday, the attorney said he was in Los Angeles with his son at the time in question.

Bad reporting, bad information and bad story by same reporter Peter Stone @McClatchyDC. No matter how many times or ways they write it, I have never been to Prague. I was in LA with my son. Proven! https://t.co/ra7nwjUA0X

However, the lack of a Czech stamp in Cohen’s passport does not necessarily rule out the possibility that he traveled to the Czech Republic.

Sources told McClatchy that Cohen traveled to Prague through Germany and did not require a passport “because both countries are in the so-called Schengen Area in which 26 nations operate with open borders.” The sources did not say whether Cohen would have used a commercial or private plane to fly to Europe, or why there does not appear to be a record of such a trip.

McClatchy notes that “it’s unclear whether Mueller’s investigators also have evidence that Cohen actually met with a prominent Russian ― purportedly Konstantin Kosachev, an ally of Russian President Vladimir Putin ― in the Czech capital.”